university of illinois frederick seitz materials research laboratory dislocation-driven surface...
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University of Illinois Frederick Seitz Materials Research Laboratory
Dislocation-DrivenDislocation-DrivenSurface Dynamics on SolidsSurface Dynamics on Solids
Sanjay V. KhareSanjay V. Khare11, Suneel Kodambaka,, Suneel Kodambaka,Wacek Swiech,Wacek Swiech, Kenji Ohmori, Ivan Petrov,Kenji Ohmori, Ivan Petrov, & Joe Greene& Joe Greene
Dept. of Materials Science and Frederick Seitz Materials Research Laboratory
University of Illinois at Urbana-Champaign
Funded by US-DOE through grant DEFG02-91ER45439
Frederick Seitz Materials Research
Laboratory
11Department of Physics and Astronomy University of Toledo
University of Illinois Frederick Seitz Materials Research Laboratory
Dislocations in solidsBulk dislocation dynamics have been extensively studied.
Surface-terminated dislocations affect nanostructural and interfacial stability, crystal growth kinetics, mechanical, chemical, & electronic properties of solids.
Bulk dislocation dynamics have been extensively studied.
Surface-terminated dislocations affect nanostructural and interfacial stability, crystal growth kinetics, mechanical, chemical, & electronic properties of solids.
Very little is known concerning the effects of dislocations on surface dynamics.
250 Å
Brune, Giovannini, Bromann, & K. Kern
Nature 394, 451 (1998)
Teng, Dove, Orme, & J.J. De Yoreo
Science 282, 724 (1998)
Spila, Desjardins, D’Arcy-Gall, Twesten, & J.E. Greene,
JAP 93, 1918 (2003)
SiGe/Si Ag/Pt KDP
University of Illinois Frederick Seitz Materials Research Laboratory
*K.F. McCarty & N.C. Bartelt: Phys. Rev. Lett. 90, 046104 (2003);Surf. Sci. 527, L203 (2003);Surf. Sci. 540, 157 (2003);Journal of Crystal Growth 270, 691 (2004).
Develop fundamental understanding of the effect of dislocations on surface dynamics
Model system: TiN
Use LEEM to investigate surface morphological evolution kinetics as a function of:
annealing timetemperature &N2 partial pressure.*
Objectives
University of Illinois Frederick Seitz Materials Research Laboratory
S. Kodambaka, N. Israeli, J. Bareño, W. Święch, K. Ohmori, I. Petrov, & J.E. Greene, Surf. Sci. 560, 53 (2004).
2D TiN(111) island decay:detachment-limited
kinetics+
highly permeable steps
2Np = 5x10-8 TorrT = 1550 K
2.8±0.3 eV2.8±0.3 eV
7.0 7.2 7.4104
105
T (K)
dA
/dt
(Å2 /s
)
1/kT (eV -1
)
1640 1600 1560
TiN/TiN(111)
University of Illinois Frederick Seitz Materials Research Laboratory
TiN/TiN(111) Spirals
field of view: 2.5 m
treal = 90 s tmovie = 9 s
T = 1688 K ~ 0.5Tm
2Np = 5x10-8 Torr
Observed during annealing in the absence of deposition/evaporation NOT BCF spirals
University of Illinois Frederick Seitz Materials Research Laboratory
• near-equilibrium*• shape-preserving• periodic• absenceabsence of applied applied
stressstress & net mass net mass change by change by deposition/evaporation.deposition/evaporation.
t = 0 s 15 s
31 s 47 s
*S. Kodambaka, V. Petrova, S.V. Khare, D.D. Johnson, I. Petrov, & J.E. Greene, Phys. Rev. Lett. 88, 146101 (2002).
= 47 s= 47 s
TiN(111) spiral step growthT = 1688 K
University of Illinois Frederick Seitz Materials Research Laboratory
TiN/TiN(111)
2Np = 5x10-8 Torr
field of view 5.6 m
treal = 650 s tmovie = 13 s
Spirals grow with a constant & 2D island areas decrease at a constant rate
T = 1670 K
2
4
6
t (
rad
ian
s)
0 60 120 180 240
4
8
12
A (
10-2
m2 )
t (s)
2
4
6
t (
rad
ian
s)
0 60 120 180 240
4
8
12
A (
10-2
m2 )
t (s)
SpiralSpiral
0 10 20 30 40
0.00
0.02
0.04
0 30 60 90
0.8
1.0
1.2
A (m
2 )
Island
t (s)
T = 1690 K
University of Illinois Frederick Seitz Materials Research Laboratory
1
10
(1
0-2 r
ad/s
)
1720 1680 1640 1600
T (K)
103
104
dA
/dt/
(1/s
)
TiN(111) spirals:TiN(111) spirals:
EEgrowthgrowth = 4.6±0.2 eV = 4.6±0.2 eV
C = 10C = 1012.6±0.612.6±0.6 s s-1-1
2D TiN(111) islands*:2D TiN(111) islands*:
EEdecaydecay = 3.1±0.2 eV = 3.1±0.2 eV
C = 10C = 1013.6±0.613.6±0.6 s s-1-1
2Np = 5x10-8 Torr
TiN/TiN(111)
*S. Kodambaka, N. Israeli, J. Bareño, W. Święch, K. Ohmori,
I. Petrov, & J.E. Greene, Surf. Sci. 560, 53 (2004).
TiN(111) spiral step kinetics is different from that of 2D islands.
University of Illinois Frederick Seitz Materials Research Laboratory
TiN/TiN(111)
2D island decay: E2D island decay: Eaa = 2.8 eV = 2.8 eV
Spiral step growth: ESpiral step growth: Edd = 4.6 eV = 4.6 eV
Ti or TiN desorption*: ETi or TiN desorption*: Eevaporationevaporation ~ 8-10 eV ~ 8-10 eV
Ea << Ed << Eevaporation*D. Gall, S. Kodambaka, M.A. Wall, I. Petrov, & J.E. Greene,
J. Appl. Phys. 93, 9086 (2003).
Spiral nucleation and growth MUST be due to bulk mass transport !!
Proposed mechanism:• driving force: bulk dislocation line energy minimization
surface spiral step formation via bulk point defect transport• dislocation cores emit/absorb point defects at a constant thermally-
activated rate.S. Kodambaka, S.V. Khare, W. Święch, K. Ohmori, I. Petrov, & J.E. Greene, Nature 429, 49 (2004).
Modeling dislocation-driven spiral growth
University of Illinois Frederick Seitz Materials Research Laboratory
Modeling dislocation-driven spiral growth
At steady state: 2iC (r) 0
eqloop l
core
ooploop
core
s
s
r
r r
r
R
2πD C(r)
k [C
r
(r )-C ]
B.C.s:
R(T) - thermally-activated point defect emission/absorption rate
C - point defect concentration (1/Å2)
Ds - surface diffusivity (Å2/s)ks - attachment/detachment rate
(Å/s) - area/TiN (Å2)
Step velocity:
eqloop lo
loop
op
loops
dr 1Ω RΩk [C(r ) -
dC =
π r]
2t
constant growth rate dA/dtconstant growth rate dA/dt
rcore
rloop
S. Kodambaka, S.V. Khare, W. Święch, K. Ohmori, I. Petrov, & J.E. Greene, Nature 429, 49 (2004).
University of Illinois Frederick Seitz Materials Research Laboratory
is a thermally-activated is a thermally-activated constantconstantAo : area outside of which R is
negligible : area/TiN (Å2) : spiral angular velocity (rad/s)R(T) : thermally-activated point defect
emission/absorption rate
o
2R
A
Total surface flux = R/Ao
1 rotation 1 ML in 2/ sec
Modeling dislocation-driven spiral growth
University of Illinois Frederick Seitz Materials Research Laboratory
1 m0 4 8 12
7
8
9
(1
0-2 r
ad/s
)
t (102 s)
decreases monotonically with annealing time
field of view 5.6 m
T = 1725 K
2Np = 5x10-8 Torr
d/dt ~ 10-5 1/s2 at 1725 K
TiN/TiN(111) vs. t
University of Illinois Frederick Seitz Materials Research Laboratory
2D TiN(111) island & spiral step kinetics are independent of N2 partial pressure
3.0
3.2
3.4
3.6
3.8
(1
0-2 r
ad/s
)
5x105x10-8-8 5x105x10-7-7
0 5 10 15 209
10
11
12
dA
/dt
(10-4
m
2 /s)
t (102 s)
vacuum
2NP (Torr)5x105x10-7-7
vacu
um
5x105x10-8-8 Torr Torr5x105x10-7-7 Torr Torr
vacuum vacuum (< 5x10(< 5x10-9 -9 TorrTorr))
1 m
T = 1670 K
TiN/TiN(111) vs. pN2
University of Illinois Frederick Seitz Materials Research Laboratory
Espiral is independent of N2 pressure & sample history
6 .8 7 .0 7 .2
0 .01
0 .1
(rad
/s)
1 /kT (1 /eV )
1720 1680 1640T (K )
4.5±0.4 eV4.5±0.4 eVat 5x10-8 Torr
4.6±0.2 eV4.6±0.2 eVin vacuum
TiN/TiN(111)
University of Illinois Frederick Seitz Materials Research Laboratory
• Investigated the nucleation & growth kinetics of TiN(111) spiral steps using HT-LEEM.
• Spiral growth is qualitatively & quantitatively different from 2D island coarsening/decay.
• Spiral growth is localized BCF growth/etch spirals.
• Angular velocity:* decreases with time irrespective of N2 pressure.
* does not vary significantly with spiral geometry.
* thermally-activated with a constant energy barrier (~ 4.5 eV), independent of the sample history & N2 pressure.
Conclusions
University of Illinois Frederick Seitz Materials Research Laboratory
LEEM – Modes of Operation
Bright Field LEEM Dark Field LEEM
Photoemission (PEEM) Mirror microscopy (MEM)
University of Illinois Frederick Seitz Materials Research Laboratory
2D TiN(111) island decay
ALL islands in the cone decay at nearly same rates
mass is not conserved locally
0 2 4 6 8
0.1
0.2
0.3
0.4
A
(m
2 )
0 1 2 3 4 5
0.2
0.4
0.6
0.8
1.0
A (m
2 )
ta (102 s)
0 2 4 6
0.1
0.2
0.3
0.4
0 2 4 6
0.1
0.2
0.3
ta (102 s)
T = 1285 oC T = 1320 oC
T = 1350 oC T = 1380 oC
University of Illinois Frederick Seitz Materials Research Laboratory
Modeling decay kinetics of islands in a cone
N. Israeli and D. Kandel, PRB 60, 5946 (1999).
r1
r2
r3
Fitting variables:
Surface diffusivitySurface diffusivity D Dss
Attachment/detachment rate KAttachment/detachment rate Kdd
Step permeabilityStep permeability p pRate of bulk transportRate of bulk transport K Kbulkbulk
Step-step interaction Step-step interaction g g
• Solve 2D steady-state diffusion eqn.:
• B.C.s: adatom fluxes at island step edges
• Derive general relation for dAi/dt
• Compare calculated r vs. t with expt.l data
2i (r) 0
University of Illinois Frederick Seitz Materials Research Laboratory
2D TiN island dynamics studies
2D island coarsening kinetics2D island coarsening kinetics(Ostwald ripening)(Ostwald ripening)
2D island coarsening kinetics2D island coarsening kinetics(Ostwald ripening)(Ostwald ripening)
Ta
ta
Surf. Sci. 526, 85 (2003).
Island shape Island shape fluctuation fluctuation
analysisanalysisPRL 88, 146101 (2002).
Equilibrium island Equilibrium island shapeshape
0
20
40
60
80
100
120
140
R110
R 100
100110
Surf. Sci. 513, 468 (2002).
2D island coalescence 2D island coalescence kineticskinetics
50 Å
Surf. Sci. 540, L611 (2003).
University of Illinois Frederick Seitz Materials Research Laboratory
0 1 2 3 4 5
8
16
24
32
0 1 2 3 4 5
8
16
24
32
Kbulk/Kd = 2.5 &
p = 0
p/Kd = 2000 & Kbulk = 0
High g, p = 0 & Kbulk =
0
TiN/TiN(111)
T = 1350 oC o LEEM data calculation
2D TiN(111) islands decay
kinetics
detachment-limited+
highly permeable steps OR
bulk diffusion
0 1 2 3 4 5
8
16
24
32
r i (10
-2 Å
)
ta (10
-2 s)
University of Illinois Frederick Seitz Materials Research Laboratory
TiN/TiN(111)
T = 1670 K
2Np = 5x10-8 Torr
field of view 5.6 m
treal = 650 s tmovie = 13 s
2
4
6
t (radians)
0 60 120 180 240
4
8
12
A (
10-2
m2 )
t (s)
Spirals grow with a constant &
2D island areas decrease at a constant rate
University of Illinois Frederick Seitz Materials Research Laboratory
1 m
TiN/TiN(111) vs. spiral geometry
field of view 5.6 m
2.10
2.16
2.22
0 5 10 151.35
1.38
1.41
t (102 s)
(
10-2 r
ad/s
)
2NP (Torr)
5x105x10-8-8 1010-7-71010-8-8< 10< 10-9-9
Spiral step velocities do not vary significantly with local environment
1650 K
1675 K